Nitrous oxide (N2O), also called laughing gas, has many applications.
It is used in particular in anesthesia and in analgesia for treating pain, for example in a mixture of about 50% by volume of N2O and 50% by volume of O2.
In anesthesia and in analgesia, the N2O-rich gas mixture is first inhaled by the patient, and a large part of the N2O is then found in the gases exhaled by the patient, mixed in particular with high proportions of CO2 and water vapor.
Thus, for a mixture containing 50% by volume of O2 and 50% by volume of N2O which is inhaled by a patient, the gases exhaled by this patient contain N2O saturated with moisture, about 4% by volume of CO2, and over 40% by volume of oxygen.
It is in fact important to remove the N2O from the gases exhaled by the patient because it risks being present in the indoor air of the buildings and accumulating therein over time.
It is in fact vitally important to prevent such an accumulation of N2O in hospital buildings, because undesirable effects have been observed during the intense and frequent inhalation of N2O, such as a vitamin B12 deficiency in the exposed persons.
N2O recovery and removal by catalysis has already been proposed, in particular by documents U.S. Pat. No. 4,259,303, WO-A-9925461, U.S. Pat. No. 2,006,008401, FR-A-2773144, JP-A-2006142160, EP-A-0698411 and JP-A-10165818.
However, this solution is complicated because it involves the use of transition metal compounds, some of which are costly and not easy to prepare. Moreover, the impurities present in the gas to be treated may poison and denature the catalyst. Besides, these methods require heating to several hundred ° C., with all the attendant complications and energy consumption.
Furthermore, document EP-A-0 995 477 proposes a method for adsorbing only small proportions of N2O present in atmospheric air, that is about a few ppm by volume. However, this document does not propose any solution for removing N2O when it is present in a volumetric proportion of several % or even several tens of %.
Accordingly, it has not hitherto been possible effectively to remove the nitrous oxide exhaled by the patient, which ends up staying in treatment rooms and similar areas of hospital buildings.
In view of this, there is a need for improved methods for treating feed gas streams containing nitrous oxide in a proportion of at least 5% by volume, preferably at least 10 to 20% by volume, in particular gas mixtures containing N2O, oxygen, water vapor and a few % of CO2, in order to increase the removal of N2O exhaled by the patients in hospital or similar buildings.